The present invention relates generally to a method and apparatus for optically measuring physical objects, particularly objects which are remote or inaccessible for direct measurement. More specifically, the invention relates to the use of a projected light raster for measuring lineal dimensions of such objects.
There frequently is a need to measure stationary or moving objects in situations where, for various reasons, the use of mechanical measuring devices is undesirable, impractical or impossible. For example, it may be necessary to measure an object which is at a distance or otherwise inaccessible, or which is radioactive or at a high temperature. A number of different optical systems have been proposed for making measurements in such situations. According to one system, for example, the size of an object moving along a path through a measuring zone is determined by photoelectrically measuring the length or degree of obscuration of a light beam directed across the zone. In such a system, if the dimensional measurement is related to the degree of obscuration, changes in light source intensity or lateral movement of the object through the measuring zone may result in inaccurate determinations. According to another system, a grid of uniformly spaced, parallel light beams is projected simultaneously across a measuring space. A dimension of an object traveling through the space is measured by counting the number of beams which are not intercepted by the object, i.e., the number which pass by the object, and are detected by a photoelectric device on the opposite side. As in the earlier-described system, the light beam source and its photoelectric detection device must be disposed on opposite sides of the measured object's travel path. This requirement prevents the use of such systems in applications where access to only one side is available.